I’m trying to find out how other Admins. go about blocking the numerous Instant Messaging Applications out on the Net (Yahoo IM, ICQ, etc..) from being use on their LANS. I used to combat this menace by blocking the various IP’s to the Messaging Servers, but this is just a temporary solution as the providers just change their DNS settings for these servers to point to a new IP and then the services goes right past the Firewall. And blocking specific ports is no help as these applications now scan for available Outbound ports and use what’s is open (i.e., http, ftp, etc..). So I’m trying to find out ways others have found to address this problem.
Any help would be much appreciated!
